Non-foaming grease-making process



2,825,692 1C6 Patented Mar. 4, 1958 NON-FOAMlNG GREASE-MAKZNG rnocnss Arnold I. Morway, Railway, N. 3., assignor to Esso Research and Engineering Company, a corporation oi Delaware No Drawing. Application May 15, B53 Serial No. 355,398

3 Claims. ({Il. 252--32) This invention relates to lubricating grease compositions. Particularly the invention relates to high temperature grease compositions, and to a process for their preparation. More particularly, the invention relates to lubricating grease compositions prepared using a complex soap, and by a process which comprises the steps of preparing a soap-oil concentrate, cooling to a temperature below the transition temperature of the complex soap without stirring, adding oil to the cooled grease cake and working the resulting mixture to obtain uniform dispersion of the soap in the added oil followed by homogenization at high rates of shear to result in a finished grease composition.

The prior art is familiar with complex soap grease compositions that have excellent high temperature properties. These prior art greases are ordinarily prepared by the saponification of a fatty acid or fat with an excess of an alkali or alkaline earth metal hydroxide in the presence of a major proportion of a mineral oil base, and heating the resulting mixture to a temperature in the vicinity of about 480 F. to 600 F. The hot fluid grease mass is then cooled with stirring to handling temperatures, usually about 200 F. to 180 F. and then is packaged. However, during the saponification and heating cycle, excessive foaming has been found to occur. As a result only a limited amount of grease can be prepared in a grease kettle. For example, in a kettle having a capacity of 16,000 pounds of grease it has only been possible to prepare a 6,000 pound batch. It has also been found necessary to discontinue the heating during the heating cycle until such time as the foaming had subsided. This results in a disproportionate amount of time being wasted during the preparation of the grease. Often this excessive foaming occurs so suddenly that overflow results. This results in material loss and is a fire hazard.

It has also been found that during the cooling cycle a viscous rubbery mass of soap-oil is formed at temperatures in the neighborhood of about 425 F. This viscous mass is very ditlicult to stir uniformly due to the tendency of the mass to stick to and climb the stirring means and to pull away from the sides of the stirring vessel. Excessive power requirements resulting from the viscosity of the mass set a very definite upper limit on the soap content of the mass. Attempts have been made to speed up the cooling cycle by passing the hot grease through a close clearance cooler such as a votator. However, when the grease entered the rubbery stage, it could not be pumped and stalled the votator.

It has now been found, and forms the object of this invention, that these Cllfi'lClllilES may be eliminated by a process which may be specifically described as follows.

A concentrated soap stock having about 50% to 60% soap is prepared in the grease kettle. Saponification is accomplished with only a minor amount of oil and a major amount of soap-forming constituents. During the saponification the tendency to foam formation is practically eliminated, and a greater volume of kettle capacity may be utilized. Lower foam formation is due to the heavy doughy nature of the soap concentrate which allows the vapors formed to pass through to the atmosphere. In prior work the heavy emulsion formed was stable and elastic.

After the saponification the soap concentrate is heated to about 500 F. and the hot molten mass is drawn into pans for cooling. When cooled, a hard soap cake is formed which shows little or no syneresis. The cooled cake is returned to the grease kettle, cut back with oil to any desired soap content and the mass is worked until the soap is evenly dispersed in the added oil. In this dilution process, suificient oil is placed in the kettle and the grease cakes added. The kettle blades will break up the cakes and disperse the soap in the oil in a somewhat heterogeneous form, but sufiicient uniform to pass to the homogenizer. Otherwise, if the oil was added to the grease, sufficient power would not be available with possible damage to the stirring mechanism. The grease is then homogenized at high rates of shear to result in a product which is uniform, non-oil separating, and has excellent structure stability and high temperature properties.

The invention described above will be more completely understood by reference to the following examples, which are illustrative only, and are not to be taken as restrictive upon the scope of the appended claims. The method of invention results in greases that have less tendency to shear harden in operating anti-friction bearings with resulting lowering in bearing operation noise.

Example 1 According to the prior art method described in detail below, 'a grease composition was prepared having the following formulation:

ingredients: Percent by weight Rapeseed oil 22.00

Sodium hydroxide 4.75 Sodium sulfonate 1.00 Phenyl alpha naphthylamine 1.00 Metal deactivator 0.50

Mineral oil (vis./2l0 F. of 50 SUS) 70.75

The rapeseed oil and one third of the mineral oil were charged to a fire-heated grease kettle of approximately three times the capacity of the grease charge and heated to F. The sodium hydroxide as a 40% aqueous solution was charged and the mass heated while stirring to saponify and to dehydrate. Above 400 F. excessive foaming occurred and it was necessary to frequently discontinue the heating until the foaming had subsided. When the temperature had reached 500 F. the fluid molten mass was pumped to a cooling kettle and cooled with stirring. Large power requirements were necessary to stir the viscous mass through the temperature of transition range, that is, from about 400 F. to 325 F. At about 235 F. the other ingredients were added and the grease was drawn, filtered and packaged. The heating and cooling cycle required from 12 to 20 hours.

Attempts to quiescently quick cool greases of the composition shown in Example 1, resulted in considerable syneresis and shrinkage of the soap structure or network due to insufiicient soap being present to give a stable product.

4 Attempts to use a high viscosity index oil or a synthetic ester lubricant as the soap menstruum were unsuccessful since the soap would not disperse in these thinner oils. However, by the instant process a low viscosity index oil may be used for preparing the concentrate and a high viscosity index oil or synthetic lubricant may be used to cut back the concentrate, since once the grease structureJis obtained, the dilution with thehigherviscosity index oil does not afiect it.

Example 2 1n accordance with.the,process of the instant invention a .=grease composition having the following formulation was prepared by the detailed procedure given below.

Ingredients: Percent by weight Rapeseed oil 50.00 Sodium hydroxide 10.80 Sodiumsulfonate 2.30 Phenyl alpha'naphthylamine 2.30 .Metal deactivator 1.10

Mineral oil(-vis./2l0 F. of 50 SUS) 33.50

The rapeseed oil and about one third of the mineral oilwer'e added to -a fire-heated grease kettle. The mass was heated to about 150 and the sodium hydroxide in the form of a "40% aqueous solution was added. The heating was continued until fluid and molten at about 500 F. There was very little'foaming during the'saponification and heatingof this sample. After reaching about 510 F. the molten 'mass was drawn into shallow pans for cooling. After cooling, the cold grease cake was returned to the kettle and worked down while additional oil was added. Sufficient oil was added to result in a soap concentration of 12.0% by weight, based on the weight of the total composition. The cut back grease was then stirred until a substantially complete dispersion of the soap in theoil was'obtained and the material was then passed through a homogenizer at a rate of shear of about 100,000 to 500,000 reciprocal seconds. The worked penetration of the grease composition was 310 mm./l0, that is, "the penetration after working for 60 strokes with the ASTM fine hole worker plate. This penetration value indicates that structurally stable greases may be prepared with this new process, at a very great saving of time. It is noted that this grease composition could not be stirred 'down through its transition temperature, i. e., 400 -F. to 325 F. in the grease kettle, due to excessive power requirements.

Example 3 According to the procedure detailed in Example 2 above, a grease composition having the following formulation was prepared:

Ingredients: Percent by weight Rapeseed oil 1 45.30

Mineral oil (vis./ 210 F. of 80 SUS) 41.25 1 48.9% soap by analysis.

This soap concentrate, or high soap content grease, was used as a base stock for the preparation of three difierent greases having different soap concentrations:

A. 60.0 weight percent of the soap concentrate of Example 3 above was cut back with 40.0 weight percent of a mineral oil having a viscosity at 210 F. of 40 SUS in a grease kettle equipped for stirring. The mass was worked until sufliciently fluid to be pumped to a milling machine were it was milled at high pressures. The milled mass was then passed through a homogenizer under a rate of shear of about 500,000 reciprocal seconds. Analysis showed that the finished grease contained 30.0 weight percent soap.

B. 50.0 weight percent of the concentrate of Example 3 was cut back with 50.0 weight percent of a mineral oil having a viscosity at 210 F. of 58. It was treated as in Example A above and analysis showed it to have a soap concentration of 25% by weight.

C; 25.0 weight percent of the soap concentrate of Example 3 was cut back with 75.0% by weight of the same mineral "on used in part'B "above. This mixture was treated as explained in part A above and analysis showed the grease to contain 13% by weight of soap.

The three grease compositions of parts A, B, and C above were submitted to the Standard ASTM grease inspections. In addition the Norma Hoflrnan oxidation test was performed on these samples. In this test a weighted sample, usually 10 grams, of the grease is placed in a steel bomb and oxygen is added until there is a stable oxygen pressure of pounds per square inch gauge. The number of hours required for the bomb pressure to drop 5 pounds per square inch is taken. Since the reduction in oxygen pressure is a function of the oxidation stability of the sample, the greater the number of hours until a 5 pound pressure drop is reached, the more stable the sample to oxidation. Results of the tests are set out in the table below.

An examination of the data of the table above shows that structurally stable, oxidation resistant grease compositions may be prepared according to the concept of this invention at a great saving of processing time. Plant outputs are also greatly increased due to more efficient utilization of plant equipment volume.

Although the examples given above show the use of a complex soap formed by the sodium hydroxide saponification of rapeseed oil, other complex soaps may also be used in the process of this invention. For instance, complexes formed from high molecular weight fatty acid soaps and low molecular weight acid salts, such as the salts of acetic, acrylic, methacrylic, furoic acid, etc. may be used. Rapesed oil that is mildly refined, but unblown, however, is the preferred embodiment.

The mineral oil base that is selected for formulating the greases in the inventive process may be chosen from wide range of oils. Oils having viscosities ranging from 40 to 200 viscosity SUS at 210 F. may be used, preferably 40 to 100 SUS at 100 F. Synthetic oils such as formals, esters, complex esters, ethers, alcohols, etc. may be used. Other soaps, including calcium complex soaps may be included. However, only unhydrolyzable material can be employed in the cooking cycle due to the large excess of caustic and high temperatures.

To reiterate briefly, the instant invention relates to an improved process for the preparation of lubricating grease compositions which comprises the steps of .preparing a complex soap concentrate containing from about 45% to 65% soap, cutting bact said concentrate with a mineral oil, and dispersing said soap in said oil by subjecting to a homogenization step at rates of shear within the range of from about 100,000 to 500,000 reciprocal seconds. More specifically, the invention relates to a process for the preparation of lubricating grease compositions for high temperature use which comprises the steps of preparing a soap concentrate containing from about 45% to 65% soap by saponifyiru a complex forming fatty material at a temperature of about F. in the presence of a minor amount of a mineral oil, heating said saponified soap to a temperature above the transition temperature of the soap, i. e., to about 500 F., drawing the molten soap into shallow pans for rapid cooling, admixing said cooled soap with additional mineral oil, dispersing said soap in said additional oil, and subjecting said mixture to a homogenizing step at a rate of shear within the range of from 100,000 to 500,000 reciprocal seconds, to obtain a finished grease composition having a soap concentration within the range of from about 8 to 35 weight percent soap, based on the weight of the total formulation. Preferred and contemplated in the preferred embodiment of this invention are the complex soaps formed by saponifying with sodium hydroxide refined unblown rapeseed oil.

Various additive materials may be added to the grease formulations to improve special qualities of the grease. The additive materials, such as metal deactivators, oxida tion inhibitors, tackiness agents, color agents, syneresis preventatives, and the like are usually added to the liquid grease at temperatures above the transition temperature of the soap or may be added as an oil-soluble concentrate in the cold homogenization step.

What is claimed is:

1. In a process for preparing soap base greases wherein the soap is formed by saponifying fatty oils with soapforming metallic hydroxides in the presence of lubricating oil and wherein the saponification is carried out at a final temperature of at least 500 F. and suflicient to cause substantial foaming, the improvement which comprises limiting the amount of lubricating oil admixed with the saponifying material during the saponification to form a soap-oil concentrate containing from to soap, cooling the hot saponified product to a solidifying temperature while maintaining said product in a quiescent state, and thereafter oiling back the soap-oil concentrate to produce a finished grease of desired soap concentration.

2. The process as defined in claim 1 wherein said fatty oil is rapessed oil.

3. The process as defined in claim 1 wherein the final grease is further homogenized at high rates of sheari References Cited in the file of this patent UNITED STATES PATENTS 2,245,772 Gothard et al June 17, 1941 2,265,791 Zirnmer et a1. Dec. 9, 1941 2,450,222 Ashburn Sept. 28, 1948 2,588,279 OHalloran Mar. 2, 1952 2,598,154 Bailey et a1. May 27, 1952 2,599,343 Morway et al. June 3, 1952 2,610,947 Morway Sept. 16, 1952 2,626,241 Sparks et al Jan. 20, 1953 OTHER REFERENCES Petroleum Engineer, vol. 22, I anuary 1950, page 0-6. 

1. IN A PROCESS FOR PREPARING SOAP BASE GREASES WHEREIN THE SOAP IS FORMED BY SAPONIFYING FATTY OILS WITH SOAPFORMING METALLIC HYDROXIDES IN THE PRESENCE OF LUBRICATING OIL AND WHEREIN THE SAPONIFICATION IS CARRIED OUT AT A FINAL TEMPERATURE OF AT LEAST 500*F. AND SUFFICIENT TO CAUSE SUBSTANTIAL FOAMING, THE IMPROVEMENT WHICH COMPRISES LIMITING THE AMOUNT OF LUBRICATING OIL ADMIXED WITH THE SAPONIFYING MATERIAL DURING THE SAPONIFICATION TO FORM A SOAP-OIL CONCENTRATE CONTAINING FROM 45 TO 65% SOAP, COOLING THE HOT SAPONIFIED PRODUCT TO A SOLIDIFYING TEMPERATURE WHILE MAINTAINING SAID PRODUCT IN A QUIESCENT STATE, AND THEREAFTER OILING BACK THE SOAP-OIL CONCENTRATE TO PRODUCE A FINISHED GREASE OF DESIRED SOAP CONCENTRATION. 